This invention concerns fuel injection systems for direct injection combustion engines, in general, and in particular, those fuel injection systems which contain valve bodies that are moveable back and forth across an operational unit in a vertical direction in the injector housing. The start of injection and the amount of fuel injected are adjusted for the injectors which are admitted into the top of the cylinder area, projecting into the individual combustion spaces of the combustion engine, and are maintained during the operation of the combustion engine. The injectors are, as a rule, fitted into the cylinder top area of the combustion engine without major structural alteration.
DE 197 01 879 A1 discloses a fuel injection system for fuel engines. The arrangement known from this reference involves a high pressure pump, which fills a fuel-fillable common high pressure container (Common Rail) with fuel. The same high pressure container is connected with an injection valve which projects into the combustion area of the engine to be fueled, the opening and closing movements of which valves are controlled by an electrically operated control valve, whereby the control valve is formed as a 3/2-way valve, which is connected to a high pressure canal flowing into an injector opening of the injector valve, by means of the injector conduit or a drainage conduit. Thereby, is provided at the control valve joint of the control valve a workspace hydraulically fillable with high pressure fuel, which is controllable for adjustment of the positioning of the control valve joint of the control valve into a drainage canal.
DE 198 35 494 A1 discloses a pump nozzle unit. This serves for the supply of fuel into a combustion space of direct injection combustion engines with a pump unit for the buildup of injection pressure and for the injection of the fuel across an injection nozzle into the combustion space. The teachings of this reference embrace, moreover, a control unit with a control valve which is formed as an outer opening A-valve, as well as a valve operational unit for control of the pressure buildup inside the pump unit. In order to provide a pump-nozzle unit with a control unit, which has a simple construction, is small in size and in particular has a short response time, it is suggested according to the present invention to form the valve operational unit as a piezoelectrically active unit.
With the configuration suggested according to the present invention of a nozzle needle of an injector for the injection of fuel into the combustion space of combustion engines, a slanted configuration can be formed for the course of the fuel injection throughout the cylinder path, and thereby the behavior of the fuel injection. The slant is formed between a control surface provided on the inside of the housing, which attaches to a control edge of the injector housing, and a conical area provided on the nozzle needle. On the side of the nozzle needle, the conical section is situated opposite the portion of the area of the borehole in the injector housing, in which the needle nozzle is moveable back and forth.
Above a constriction in the nozzle needle there is located an upper management section of the nozzle needle. Free surfaces are provided inside this upper management section, across which the fuel can flow from the nozzle space into which it enters under high pressure from the high pressure collecting area, in the direction of the point of the nozzle needle. In more advantageous manner, the management section of the nozzle needle provided by means of the mentioned free surfaces, defines a ring shaped canal. The ring shaped canal functions between a straight surrounding section of the nozzle needle and a front surface section of the wall of the housing, as a throttle element next to the lower end of the nozzle needle, which thanks to its conical formation likewise functions as a throttle element. Across the ring shaped canal which functions as a throttle element, there enters during a first partial stroke of the nozzle needle within the injector housing only a small volume of fuel into the combustion space of the combustion engine. In this manner, a continuous ignition delay can be set at the start of the injection operation up until complete development of the flame front in the combustion space. Through further elevation of pressure at the pressure stage of the nozzle needle in the nozzle space, the nozzle needle will be upwardly driven towards the effect of the thick spring, so as to produce during the further cylinder path of the nozzle needle, a gradual widening of the distance between the control surface provided in the wall of the housing and the conical area of the nozzle needle. The result is that from the start of the spraying, the effective ring shape canal is continuously widened during the further cylinder path of the nozzle needle and a greater volume of fuel can be transported. The increase in the amount of injected fuel obtainable by means of the conical surface of the nozzle needle is implemented first after a complete formation of the flame front in the combustion space, so that the ignition delay disappears and an increased volume of fuel will be sprayed at the right time into the combustion space of the combustion engine, namely when the thermodynamic conditions are optimal therefor.
An accurate prescription for the course of the pressure buildup during the injection phase depends upon the length of the slope of the conical area of the nozzle needle, furthermore on the angle of the pitched surface relative to the front surface, and upon the vertical cylinder path of the nozzle needle within the injector housing.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.